A video camera holds images data provided by a CCD (charge coupled device) solid state image pickup device by a frame memory and compresses blocks of image data by a MPEG (Moving Picture Experts Groups) method. An electronic still camera, similarly to the video camera, holds image data provided by a CCD solid state image pickup device by a frame memory and compresses blocks of image data by a JPEG (Joint Photographic Experts Group) method.
In recent years, CMOS solid state image pickup devices have been put to practical use. FIG. 1 shows the characteristics of the CCD solid state image pickup device in comparison with those of the CMOS image pickup device. As shown in FIG. 1, the CMOS image pickup device has many distinctive characteristics. For example, whereas the CCD image pickup device uses the same charge storage start and end times for all pixels, the CMOS image pickup device used different charge storage start and end times for different columns or pixels.
Particularly, whereas the CCD image pickup device reads data on pixels in a serial transmission mode as shown in FIG. 2, the CMOS image pickup device can read data on pixels in an X-Y address control mode as shown in FIG. 3. Thus the degree of freedom of reading of the CMOS image pickup device is higher than that of the CCD image pickup device. FIG. 2 is a typical view illustrating a mode of output of image data from the CCD image pickup device. In the CCD image pickup device, charges held by the pixels are transferred to a vertical transfer register, the transferred charges are transferred sequentially to a horizontal transfer resister and the horizontal transfer resister provides the charges sequentially as shown in FIG. 2. FIG. 3 is a typical view illustrating a mode of output of image data from the CMOS image pickup device. In the CMOS image pickup device, charges held by pixels on each column are provided sequentially.
More concretely, in the CMOS image pickup device, MOSFETs included in pixels are selectively turned on by horizontal address lines and vertical address lines to send out image data from the selected pixels to signal lines. In the CMOS image pickup device shown in FIG. 3 by way of example, a plurality of pixels successively arranged on each vertical line use one signal line for one column line, the respective conditions of the horizontal address lines respectively corresponding to the pixels on each column line are changed sequentially to turn on the MOSFETs included in those pixels sequentially. Thus the column line is assigned to the pixels successively arrange in a vertical direction in a time-sharing mode to send out image data from the pixels. The pixels successively arranged on each horizontal line are connected to each horizontal address line. Therefore, the assignment of the pixels successively arranged in a vertical direction to the column line in a time-sharing mode is carried out simultaneously for the pixels successively arranged in a horizontal direction to provide image on each line.
A CMOS image pickup device similar to the foregoing CMOS image pickup device and peripheral circuits are proposed in, for example, JP 2004-31785 A.
Various coding methods relating to such image data processing have been proposed. Those coding methods uses a wavelet transform process. The wavelet transform process divides high-frequency image data and low-frequency image data by a band division process with respect to the horizontal and the vertical direction, divides the image data into four subbands by down sampling. For example, the band division process is performed once to divide image data into four subbands HH, HL, LH and LL as shown in FIG. 4(A) or the band division process is repeated to divide image data into subbands as shown in FIG. 4(B). FIG. 4(B) shows the results of repetition of the band division process three times. The subband LL having a low frequency with respect to the horizontal and the vertical direction among the subbands HH, HL, LH and LL is subjected to the band division process to divide the subband LL into four subbands LLHH, LLHL, LLLH and LLLL, and the subband LLLL having a low frequency with respect to the horizontal and the vertical direction among the subbands LLHH, LLHL, LLLH and LLLL is subjected to the band division process into four subbands LLLLHH, LLLLHL, LLLLLH and LLLLLLL.
Previously proposed wavelet transform processes for the coding process includes a line-base wavelet transform process that processes image data on each of lines and a tile-base wavelet transform process that processes image data on each of tiles, namely rectangular blocks defined in each of pictures.
It is expected that the construction of the imaging apparatus can be further simplified and the rate can be controlled more properly by a simple process as compared with a known process if the high degree of freedom of reading image data characterizing the MOS image pickup device, can be effectively used. Incidentally, different parts of an image have different degrees of coding difficulty. Therefore, if a coding process uses the MPEG method, fine rate control is performed by, for example, a TM5 method (test mode 5 method).